[Nut-upsuser] Server not shutting down before power loss

Julian H. Stacey jhs at berklix.com
Tue Dec 29 00:38:10 UTC 2015

> Hi I hope someone can please help.
> I have an Ubuntu Server running 14.04.3 LTS and using an APC ES550 UPS
> connected via USB.
> I've installed Nut and can see it does monitor the UPS correctly and give
> the correct stats with battery percentage etc.
> But on doing a "real" test and unplugging the UPS from the power supply,
> after watching the battery drop slowly suddenly the server just lost power
> along with the UPS and monitor. No graceful shutdown and I didn't see any
> attempt at a warning or shutdown in any way.
> Now I realise my UPS is no use at all if my system doesn't shutdown.
> Can anyone please help me get this to work as I'm vulnerable at present.

Chuckle. I remember a previous New Year I said "Watch This" pulled the plug,
& what visitors expected & I did Not ... Happened ... All disc spun down.
Demo effect ! I hadnt checked batteries for a while.

As ever, as I & others have commented over years in archives,
first disconnect batteries & check voltage of each battery, - dead easy,

Then much more important: calculate internal resistance of each battery.
Batteries go bad after some years, even on trickle charge.
Measure voltage drop when driving a load such as 1 or a few car
headlamp bulbs in parallel. Then its simply Ohms law V=IR,

If voltage drops from say 13V to 11V & if you use 1 headlamp that
uses maybe 4 amps, then 13-11 / 4 = 2/4 = 0.5 which is on high side,
you dont want higher, better 0.3 or less.

Your UPS for PC's will prob. want a lot more than 4 amps, so low 
internal resistance is critical to good UPS performance.

If you decide to use computer as your measurement load instead or
a car headlamp bulb, remember the static inverter is still On,
generating 110 or 240 Volts, dont kill yourself or blow stuff up
while measuring :-)

> Nut Version: 2.7.1-1ubuntu1
> Nut installation method was just through apt from standard Ubuntu repos.
> Thanks very much indeed.

Julian Stacey,  BSD Linux Unix Sys. Eng. Consultant Munich http://berklix.com
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